Diabetic retinopathy is a leading cause of blindness. Prior studies implicate that, early in the disease process; chronic inflammation damages the capillaries in the retina. This leads to retinal ischemia and, over many years, proliferation of new blood vessels into the vitreous. Bleeding from the new vessels limits vision. There is great clinical need for therapies to prevent or slow the progression of the disease, and early intervention to reduce the inflammation may be beneficial. Leukotrienes, metabolites of arachidonic acid, are potent mediators of inflammation in several diseases from asthma to atherosclerosis. In mice, deficiency of leukotrienes protects the retina from capillary degeneration. The goal of this proposal is to investigate the FDA-approved leukotriene inhibitors, zileuton and montelukast, for efficacy in the treatment of diabetic retinopathy in mice. In Specific Aim 1, diabetic mice will be administered zileuton or montelukast for 2 months with assessment of the typical diabetes-induced increases in retinal leukocyte adherence, superoxide production, NFkB-mediated inflammatory gene transcription, and vascular permeability, and for 9 months with evaluation of retinal histopathology. Specific Aim 2 will investigate three mechanisms by which leukotrienes may regulate chronic inflammation in the diabetic retina: 1) autocrine: leukocytes may generate increased superoxide and leukotriene B4 through autoamplification, 2) paracrine: leukocytes may secrete leukotriene B4 which induces retinal micro vascular endothelial cell expression of ICAM1 and additional superoxide generation, and 3) transcellular metabolism: retinal microvascular endothelial cells and glial cells synthesize leukotrienes following transfer of leukotriene A4, generated by the leukocyte, which may further amplify the inflammatory signal within the retina itself. Assays to detect cell death, superoxide, and inflammatory markers will be performed on leukocyte and retinal microvascular endothelial cells in co-culture. To the co-culture system, selective leukotriene inhibitors or targeted siRNA transfections will be employed to determine the mechanism of leukotriene action, which will further guide therapeutic intervention. In Specific Aim 3, leukocytes will be isolated from human subjects with diabetes mellitus of varying glycemic control. Measurements of superoxide and leukotriene B4 generation will be performed before and after treatment with zileuton or montelukast for 3 months. The study of the efficacy and mechanism of action of clinically approved leukotriene inhibitors to prevent diabetic retinopathy in the mouse coupled with a potential screening tool for use in human subjects will provide the necessary information for translation of this work to patient care.